On some transmissions, the torque converter clutch (TCC) could still have capacity even though the pressure is commanded to 0 kPa, which is impacting on the TCC behavior. This problem leads to a TCC chuggle phenomenon at low torque (engine speed waving). It also degrades the performance of the electronically commanded converter clutch (abbreviated EC3, which means that the torque converter clutch is controlled in order to regulate the torque converter) in coast conditions.
An existing calibration solution is a so-called TCC immediate off low torque feature which fixes the chuggle issue by releasing the TCC (off mode), but does not meet the customer expectations on coast EC3 performance and therefore is insufficient.
Another approach is to re-adjust the calibration based on the transmissions that have a minimum TCC offset. This solves coast EC3 performance and chuggle problems on the transmissions with a minimum TCC offset (marginal amount of the production), but damages the TCC behavior of the “nominal offset” transmissions (majority of the production). The transmissions with a minimum TCC offset are those transmissions whose TCC transmits some torque, even if the minimal pressure is commanded.
In EP 1 739 329 A2, a torque converter connecting an engine and a transmission of a vehicle is provided with a lockup clutch and a controller is programmed to increase an engagement force of a lockup clutch under open loop control before shifting to feedback control on the engaging force using a target slip rotation speed. When an engine torque rapidly decreases during open loop control, the controller decreases the engaging force according to a variation amount of the engine output torque, thereby preventing an unintentional sudden engagement of the lockup clutch due to decrease in the engine output torque.
Document JP 2005291345 A describes a control device for an automatic transmission with an input torque detecting means for detecting input torque to a torque converter, a real differential pressure computing means for computing real differential pressure on the basis of the input torque when fastening of a lock-up clutch is concluded, a learning value computing means for computing a difference between a differential pressure command value and the real differential pressure when fastening of the lock-up clutch is concluded as a learning value, and a learning value housing means for storing the learning value in relation to the differential pressure command value. A learning correcting means corrects the differential pressure command value by reading a learning value corresponding to the differential pressure command value from the learning value housing means.
In view of the foregoing, at least one objective of the invention is to avoid that the torque converter clutch still has capacity even if the pressure is commanded to be zero without modifying the behavior of the torque converter clutch behavior of all the production. In addition, other objectives, desirable features, and characteristics will become apparent from the subsequent summary and/or detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background.